How necessary is polyfill in a sonosub design? (1 Viewer)

[Mike Dr]

I'm almost done with my tempest sonosub. I did not account for any polyfill in my designs, and just wanted to know if I would benefit from polyfill, or rather if there will be anything "bad" if I dont have polyfill...

 

[Harry Lincoln]

Mike, I'm assuming your sub is ported. Its best to cover the inner wall of the sonotube and outer wall of the port with polyester batting(I'm not sure if this is the same as polyfill). I also covered the underside of the top endcap. The polyester I used was about 1 - 1.5 inches thick, picked it up at a fabric store. Its a lot easier to put it in now rather than pull the sub apart to add it later.

Harry.

 

[Mike Dr]

How will the addition of polyfill (what is it called in the store by the way?) affect the response that was designed in LSPCad with 0% polyfill?

 

[Patrick Sun]

It's called polyfill (or pillow stuffing).

You can model the effect of stuffing by changing the percentage of the stuffing parameter. Use 16 ounces of stuffing per cubic foot as being 100% stuffed. So if you use 8 ounces of stuffing per cubic foot, you have the enclosure 50% stuffed.

 

[Mike Dr]

anyone wanna help me out w/ measurements?
my sub is as follows:
50" high, 18.9" inner diameter
4" port 10" length
subtract about 7 liters for inner amp enclosure.
Top plug is .75, cap is 1.5 (port cap)
botttom plug is 1.5", cap is 2.25 (driver cap)
*cap is the whole, plug is the part inside the tube
driver is a tempest
my measured design was for a 214 liter enclosure with approximately an 18hz tuning frequency
thanks

 

[Jedd]

You can model the effect of stuffing by changing the percentage of the stuffing parameter. Use 16 ounces of stuffing per cubic foot as being 100% stuffed. So if you use 8 ounces of stuffing per cubic foot, you have the enclosure 50% stuffed

Help says if you cnahge % of stuffing, you need to change QB value. The bigger % the smaller QB. My results for 88L sealed shiva (SPL, excurtion):
fill = 100%, QB = 3:
20Hz - 104.2 Db, 28.5 mm
40Hz - 110.2 Db, 20.1 mm
fill = 50%, QB = 7:
20Hz - 104.3 Db, 29.0 mm
40Hz - 110.6 Db, 21.5 mm
fill = 0%, QB = 15:
20Hz - 104.2 Db, 28.7 mm
40Hz - 110.8 Db, 22.0 mm
So, why to care about stuffing at all?

 

[ThomasW]

Why care about adding damping material ?
Link Removed and HERE are why

 

[Mike Dr]

Thomas - in the first link, it's stated that damping is more important in a small box .. in the second it shows the negative effects of over-damping... in either case, it seems that stuffing is not THAT important for an enclosure of the size that I have.. i already put some poly fill stuff i had left over from a car subwoofer project around the port and i think i'll put some around the inner amp enclosure and maybe on the caps...

Lining the walls would be kinda tricky at this point

 

[Jedd]

The first link tells me that if I fill my 3ft^ box with 4.5 pounds of polyfill I'll gain 30%...

So why there is no changes in the lspCAD? What do I miss?

 

[ThomasW]

Guys
Don't overthink this stuff. Damping helps in several ways. so EXPERIMENT
To line a tube get the batting not the loose fill. Form it into a blanket, roll that up and slide it into the tube. To attach it, staple the upper and lower edges of the batting to the top and bottom endcaps.
For a box sub just staple gun it the the walls

 

[Mike Dr]

Thomas, actually I found a way to work with the loose stuff since i had a bunch of it sitting around.. I put a bunch around my port by spraying it with 3M adhesive, pressing relatively equal ammounts of it all around it, and then surround the whole thing with fiberglass mesh .. I will post pics of everything once I'm done with the sub, or if someone really wants to see it I can post just those. The mesh is very light and I doubt it will do anything to sound.

 

[Ryan Schnacke]

It seems to be a common belief today that vented enclosures should be lined with heavy damping material of one kind or another. While this procedure may be of some benifit to poorly designed, or improperly tuned systems, it should be unnecessary if proper design procedures are followed. The minimal damping required to eliminate unwanted midrange port radiation should be choosen carefully to ensure that it has little effect on absorption of acoustic energy at frequencies near and just above Fb.

So what I'm hearing is - if you want to cheat you can stuff the box a bit and go with a smaller box, but that's not the preferred method.

 

[ThomasW]

I line ALL my ported designs with high wool content felt gasket material. This material isn't for the faint of heart given the $11-17/sq ft cost.

It's not being done to 'cheat' the box size. It's done because it absorbs the higher frequencies not filtered out by the XO. As a result it improves the quality of the sound.

For those wanting a less expensive material the 2.5" acoustic foam from PE works well too.

Both poly batting and fiberglass can be used but I breakout in a rash just looking at 'glass'

 

[Ryan Schnacke]

Gotcha. Thanks for your input Thomas.

 

[Jedd]

And I really don't know how well UNIBOX models stuffing.

Do you know how well lspCAD models the stuffing?

For the sealed 3ft^3, I don't see any dB changes at all (stuffed from 0% to 100%)

 

[Ryan Schnacke]

No idea. Sorry.

 

[SteveF]

Tom Nousaine wrote a very useful article on stuffing that
may be of interest to you:
Link Removed

 

[ThomasW]

Steve
A link to that Nousaine webpage was posted earlier in this thead

 

[Jedd]

The problem is that Tom says one thing and my lspCAD displays totaly different thing. Whom to trust?

 

[Patrick Sun]

This is yet another example of "paralysis by analysis". Just build it and enjoy it. Nothing is ever perfect the 1st time around, it's how you gain experience. Don't be afraid to try and fail.